The present invention relates to an apparatus for determining the interfacial tension between any two polymer melts, and for determining properties of relaxation in extension of the system comprising the same two polymer melts.
Spinning rod tensiometers have been advanced. U.S. Pat. No. 4644782 discloses a spinning rod interfacial tensiometer utilizing a central rod in a housing. This device works well for certain applications, but when trying to determine the interfacial tension and relaxation time for two polymers, heat must be provided to the system. An adequate opening must also be left for taking measurements of the drop that is formed by the less dense of the polymers. With viscous polymers, the spin-up does not create problems, such as having the less dense polymer thrown to the outside, and because the final speeds are very high, the diameter to be measured can be quite small. The rod in the center of the tube can be used to measure index of refraction, but the rod is not used for measuring the other properties such as interfacial tension and relaxation times for extensional deformation of a blend of two polymers, according to the present invention.